Metabolic actions of insulin in men and women

Plasma amino acid levels are elevated in young, healthy low birth weight men exposed to short-term high-fat overfeeding

Low birth weight (LBW) individuals exhibit a disproportionately increased, incomplete fatty acid oxidation and a decreased glucose oxidation, compared with normal birth weight (NBW) individuals, and furthermore have an increased risk of developing insulin resistance and type 2 diabetes. We hypothesized that changes in amino acid metabolism may occur parallel to alterations in fatty acid and glucose oxidation, and could contribute to insulin resistance. Therefore, we measured fasting plasma levels of 15 individual or pools of amino acids in 18 LBW and 25 NBW men after an isocaloric control diet and after a 5-day high-fat, high-calorie diet. We demonstrated that LBW and NBW men increased plasma alanine levels and decreased valine and leucine/isoleucine levels in response to overfeeding. Also, LBW men had higher alanine, proline, methionine, citrulline, and total amino acid levels after overfeeding compared with NBW men. Alanine and total amino acid levels tended to be negatively associated with the insulin-stimulated glucose uptake after overfeeding. Therefore, the higher amino acid levels in LBW men could be a consequence of their reduction in skeletal muscle insulin sensitivity due to overfeeding with a possible increased skeletal muscle proteolysis and/or could potentially contribute to an impaired insulin sensitivity. Furthermore, the alanine level was negatively associated with the plasma acetylcarnitine level and positively associated with the hepatic glucose production after overfeeding. Thus, the higher alanine level in LBW men could be accompanied by an increased anaplerotic formation of oxaloacetate and thereby an enhanced tricarboxylic acid cycle activity and as well an increased gluconeogenesis.

The Mitochondrial Lon Protease Is Required for Age-Specific and Sex-Specific Adaptation to Oxidative Stress

Multiple human diseases involving chronic oxidative stress show a significant sex bias, including neurodegenerative diseases, cancer, immune dysfunction, diabetes, and cardiovascular disease. However, a possible molecular mechanism for the sex bias in physiological adaptation to oxidative stress remains unclear. Here, we report that Drosophila melanogaster females but not males adapt to hydrogen peroxide stress, whereas males but not females adapt to paraquat (superoxide) stress. Stress adaptation in each sex requires the conserved mitochondrial Lon protease and is associated with sex-specific expression of Lon protein isoforms and proteolytic activity. Adaptation to oxidative stress is lost with age in both sexes. Transgenic expression of transformer gene during development transforms chromosomal males into pseudo-females and confers the female-specific pattern of Lon isoform expression, Lon proteolytic activity induction, and H₂O₂ stress adaptation; these effects were also observed using adult-specific transformation. Conversely, knockdown of transformer in chromosomal females eliminates the female-specific Lon isoform expression, Lon proteolytic activity induction, and H₂O₂ stress adaptation and produces the male-specific paraquat (superoxide) stress adaptation. Sex-specific expression of alternative Lon isoforms was also observed in mouse tissues. The results develop Drosophila melanogaster as a model for sex-specific stress adaptation regulated by the Lon protease, with potential implications for understanding sexual dimorphism in human disease.

Sex differences in insulin sensitivity and insulin response with increasing age in black South African men and women

AIMS

Black Africans are disproportionally affected by type 2 diabetes, but the pathophysiology is poorly understood. The study aimed to examine the effect of sex and age on insulin sensitivity and insulin response in black South African adults.

METHODS

This cross-sectional study included a random sample of 179 men and 260 women aged 25-74years with normal glucose tolerance from 5 peri-urban townships in Cape Town, SA. Insulin sensitivity (insulin sensitivity index, ISI_0,120) and response (insulinogenic index, IGI), and the disposition index (DI, ISI_0,120×IGI), derived from an oral glucose tolerance test, were measured.

RESULTS

Although men were older (median [interquartile range]: 39 [30-48] vs. 35 [29-44], P=0.021) and had significantly lower BMI than women (22.6 [20.0-25.3] vs. 31.0 [25.9-35.7] kg/m², P=0.001), DI was not different (P=0.740), but ISI_0,120 was higher (P=0.007) and IGI was lower (P=0.074) in men than women, adjusting for age and BMI. With increasing age, DI (β (95%CI): -24.4 (-36.3 to -12.5), P<0.001) and IGI (β (95%CI): -4.9 (-7.5 to -2.2), P<0.001) decreased similarly in both sexes, but ISI_0,120 did not change (β (95%CI): 0.005 (-0.20 to 0.03), P=0.675).

CONCLUSION

Black South African women with normal glucose tolerance have lower insulin sensitivity than their male counterparts, but increase their insulin response to maintain normoglycemia. With increasing age, insulin sensitivity remains unchanged, but the insulin response decreases at a similar rate in men and women.

The relationship between cholesterol concentration and carotid intima media thickness differs according to gender and menopausal status in Korean type 2 diabetic patients

BACKGROUND

We investigated the associations between cardiometabolic factors and carotid intima media thickness (IMT) in Korea type 2 diabetes (T2DM) patients, and assessed the possible difference with respect to gender and menopausal status.

METHODS

We conducted a cross-sectional study with 1288 T2DM patients from the Department of Endocrinology and Metabolism at Gangnam Severance Hospital. Carotid IMT and various biochemical parameters were measured, and the postmenopausal status was assessed.

RESULTS

In partial correlation analysis, total cholesterol (TC) and LDL cholesterol (LDL-C) were positively correlated with right maximum IMT in men. For postmenopausal women, TC and LDL-C were positively correlated with IMT (all p<0.05) while no such correlation was observed in premenopausal women. In regression analysis, age was the most predominant factor for IMT in all 3 groups. For men, insulin and TC were predictive factors for maximum IMT (all p<0.05), and for postmenopausal women, TC and LDL-C were significant factors for mean and maximum IMT (all p<0.01). However, cholesterol concentrations were not related to all types of IMT in premenopausal women.

CONCLUSION

The association between LDL-C and carotid IMT seems to differ according to gender and menopausal status in T2DM patients.

Total cholesterol as a risk factor for coronary heart disease and stroke in women compared with men: A systematic review and meta-analysis

BACKGROUND

Raised total cholesterol is a strong risk factor for cardiovascular disease (CVD). It remains unknown whether sex differences exist in the relationship between total cholesterol and CVD outcomes.

METHODS

PubMed was searched in December 2014 for cohort studies reporting on the relationship between total cholesterol and coronary heart disease (CHD) and total stroke, separately in men and women. Random effects meta-analyses with inverse variance weighting were used to obtain adjusted pooled sex-specific relative risks (RR) and women-to-men ratio of RRs (RRRs).

RESULTS

Data from 97 cohorts, 1,022,276 individuals, and 20,176 CHD and 13,067 stroke cases were included. The pooled RR (95% confidence interval) for CHD associated with a 1-mmol/L increase in total cholesterol was 1.20 (1.16; 1.24) in women and 1.24 (1.20; 1.28) in men, resulting in a RRR of 0.96 (0.93; 0.99). Corresponding RRs for the risk of total stroke were 1.01 (0.98; 1.05) in women, and 1.03 (1.00; 1.05) in men, with a pooled RRR of 0.99 (0.93; 1.04). Pooled RRRs (95% CI) comparing individuals in the highest TC category to those in the lowest, such as the highest versus lowest third, were 0.87 (0.79; 0.96) for CHD and 0.86 (0.76; 0.97) for total stroke.

CONCLUSION

Raised total cholesterol is a strong risk factor for CHD, with evidence of a small, but significantly stronger, effect in men compared to women. Raised total cholesterol had little effect on the risk of total stroke in both sexes.

Effects of estradiol, estrogen receptor subtype-selective agonists and genistein on glucose metabolism in leptin resistant female Zucker diabetic fatty (ZDF) rats

The leptin resistant Zucker diabetic fatty (ZDF) rats are hyperphagic and become obese, but whereas the males develop type 2 diabetes mellitus (T2DM), the females remain euglycaemic. As estrogen deficiency is known to increase the risk of developing T2DM, we evaluated the role of ER subtypes alpha and beta in the development of glucose tolerance in leptin resistant ovariectomized (OVX) ZDF rats. At least six rats per group were treated with either vehicle (OVX), 17β-estradiol (E2), ER subtype-selective agonists (Alpha and Beta), or genistein (Gen) for 17 weeks. At the end of the treatment period a glucose tolerance assay was performed and the metabolic flux of (13)C-glucose for the E2 group was investigated. OVX ZDF rats treated with E2, Alpha, Beta, and Gen tolerated the glucose significantly better than untreated controls. E2 treatment increased absorbance/flux of (13)C-glucose to metabolic relevant tissues such liver, adipose tissue, gastrocnemius, and soleus muscle. Moreover, whereas Alpha treatment markedly increased mRNA expression of GLUT4 in gastrocnemius muscle, Beta treatment resulted in the largest fiber sizes of the soleus muscle. Treatment with Gen increased both the mRNA expression of GLUT 4 and the fiber sizes in the skeletal muscle. In addition, E2 and Alpha treatment decreased food intake and body weight gain. In summary, estrogen-improved glucose absorption is mediated via different molecular mechanisms: while activation of ER alpha seems to stimulate muscular GLUT4 functionality, activation of ER beta results in a hypertrophy of muscle fibers. In addition, selective activation of ER alpha decreased food intake and body weight gain. Our data further indicate that ER subtype-selective agonists and genistein improve systemic glucose tolerance also in the absence of a functional leptin signaling pathway.

Metabolically Healthy Obesity Is Not Associated with Food Intake in White or Black Men

BACKGROUND

Healthy obese individuals may be protected against adverse health outcomes. Diet and race might influence healthy obesity, but data on their roles and interactions on the phenotype are limited.

OBJECTIVE

We compared the food intake of metabolically healthy obese men to those of other weight status-metabolic health phenotypes.

METHODS

Men (n = 4855) aged ≥ 45 y with BMI ≥ 18.5 kg/m(2) and free of cardiovascular diseases, diabetes, and cancer were evaluated in a cross-sectional study of the REGARDS (REasons for Geographic And Racial Differences in Stroke) study cohort. Food intake was assessed with the use of a food frequency questionnaire. Weight status-metabolic health phenotypes were defined by using metabolic syndrome (MetS) and homeostasis model assessment of insulin resistance (HOMA-IR) criteria. Mean differences in food intake among weight status-metabolic health phenotypes were compared with the use of linear regression.

RESULTS

MetS-defined healthy obesity was present in 44% of white obese men and 58% of black obese men; the healthy obese phenotype, based on HOMA-IR, was equally prevalent in both white (20%) and black (21%) obese men. Among white men, MetS-defined healthy and unhealthy obesity were associated with lower wholegrain bread intake and higher consumption of red meat (P < 0.001), whereas HOMA-IR-defined healthy and unhealthy obesity were associated with lower red meat intake (P < 0.0001) compared with healthy normal weight in multivariable-adjusted analyses that adjusted for sociodemographic, lifestyle, and clinical confounders. However, results were attenuated and became nonsignificant after further adjustment for BMI. Healthy and unhealthy overweight, defined by both criteria, were associated with lower whole grain bread intake (P < 0.001) in all models. Among black men, weight status-metabolic health phenotypes were not associated with food intake in all models.

CONCLUSION

Healthy obesity in men is not associated with a healthier diet. Future studies need to consider dietary patterns, which may better inform the holistic effect of diet on healthy obesity, in prospective analyses.

The impact of sleep on age-related sarcopenia: Possible connections and clinical implications

Sarcopenia is a geriatric condition that comprises declined skeletal muscle mass, strength and function, leading to the risk of multiple adverse outcomes, including death. Its pathophysiology involves neuroendocrine and inflammatory factors, unfavorable nutritional habits and low physical activity. Sleep may play a role in muscle protein metabolism, although this hypothesis has not been studied extensively. Reductions in duration and quality of sleep and increases in prevalence of circadian rhythm and sleep disorders with age favor proteolysis, modify body composition and increase the risk of insulin resistance, all of which have been associated with sarcopenia. Data on the effects of age-related slow-wave sleep decline, circadian rhythm disruptions and obstructive sleep apnea (OSA) on hypothalamic-pituitary-adrenal (HPA), hypothalamic-pituitary-gonadal (HPG), somatotropic axes, and glucose metabolism indicate that sleep disorder interventions may affect muscle loss. Recent research associating OSA with the risk of conditions closely related to the sarcopenia process, such as frailty and sleep quality impairment, indirectly suggest that sleep can influence skeletal muscle decline in the elderly. Several protein synthesis and degradation pathways are mediated by growth hormone (GH), insulin-like growth factor-1 (IGF-1), testosterone, cortisol and insulin, which act on the cellular and molecular levels to increase or reestablish muscle fiber, strength and function. Age-related sleep problems potentially interfere intracellularly by inhibiting anabolic hormone cascades and enhancing catabolic pathways in the skeletal muscle. Specific physical exercises combined or not with nutritional recommendations are the current treatment options for sarcopenia. Clinical studies testing exogenous administration of anabolic hormones have not yielded adequate safety profiles. Therapeutic approaches targeting sleep disturbances to normalize circadian rhythms and sleep homeostasis may represent a novel strategy to preserve or recover muscle health in older adults. Promising research results regarding the associations between sleep variables and sarcopenia biomarkers and clinical parameters are required to confirm this hypothesis.

Does epigenetic dysregulation of pancreatic islets contribute to impaired insulin secretion and type 2 diabetes?

β cell dysfunction is central to the development and progression of type 2 diabetes (T2D). T2D develops when β cells are not able to compensate for the increasing demand for insulin caused by insulin resistance. Epigenetic modifications play an important role in establishing and maintaining β cell identity and function in physiological conditions. On the other hand, epigenetic dysregulation can cause a loss of β cell identity, which is characterized by reduced expression of genes that are important for β cell function, ectopic expression of genes that are not supposed to be expressed in β cells, and loss of genetic imprinting. Consequently, this may lead to β cell dysfunction and impaired insulin secretion. Risk factors that can cause epigenetic dysregulation include parental obesity, an adverse intrauterine environment, hyperglycemia, lipotoxicity, aging, physical inactivity, and mitochondrial dysfunction. These risk factors can affect the epigenome at different time points throughout the lifetime of an individual and even before an individual is conceived. The plasticity of the epigenome enables it to change in response to environmental factors such as diet and exercise, and also makes the epigenome a good target for epigenetic drugs that may be used to enhance insulin secretion and potentially treat diabetes.

Mitochondrial maintenance failure in aging and role of sexual dimorphism

Gene expression changes during aging are partly conserved across species, and suggest that oxidative stress, inflammation and proteotoxicity result from mitochondrial malfunction and abnormal mitochondrial-nuclear signaling. Mitochondrial maintenance failure may result from trade-offs between mitochondrial turnover versus growth and reproduction, sexual antagonistic pleiotropy and genetic conflicts resulting from uni-parental mitochondrial transmission, as well as mitochondrial and nuclear mutations and loss of epigenetic regulation. Aging phenotypes and interventions are often sex-specific, indicating that both male and female sexual differentiation promote mitochondrial failure and aging. Studies in mammals and invertebrates implicate autophagy, apoptosis, AKT, PARP, p53 and FOXO in mediating sex-specific differences in stress resistance and aging. The data support a model where the genes Sxl in Drosophila, sdc-2 in Caenorhabditis elegans, and Xist in mammals regulate mitochondrial maintenance across generations and in aging. Several interventions that increase life span cause a mitochondrial unfolded protein response (UPRmt), and UPRmt is also observed during normal aging, indicating hormesis. The UPRmt may increase life span by stimulating mitochondrial turnover through autophagy, and/or by inhibiting the production of hormones and toxic metabolites. The data suggest that metazoan life span interventions may act through a common hormesis mechanism involving liver UPRmt, mitochondrial maintenance and sexual differentiation.

Comparative Meta-Analysis of Transcriptomics Data during Cellular Senescence and In Vivo Tissue Ageing

Several studies have employed DNA microarrays to identify gene expression signatures that mark human ageing; yet the features underlying this complicated phenomenon remain elusive. We thus conducted a bioinformatics meta-analysis on transcriptomics data from human cell- and biopsy-based microarrays experiments studying cellular senescence or in vivo tissue ageing, respectively. We report that coregulated genes in the postmitotic muscle and nervous tissues are classified into pathways involved in cancer, focal adhesion, actin cytoskeleton, MAPK signalling, and metabolism regulation. Genes that are differentially regulated during cellular senescence refer to pathways involved in neurodegeneration, focal adhesion, actin cytoskeleton, proteasome, cell cycle, DNA replication, and oxidative phosphorylation. Finally, we revealed genes and pathways (referring to cancer, Huntington's disease, MAPK signalling, focal adhesion, actin cytoskeleton, oxidative phosphorylation, and metabolic signalling) that are coregulated during cellular senescence and in vivo tissue ageing. The molecular commonalities between cellular senescence and tissue ageing are also highlighted by the fact that pathways that were overrepresented exclusively in the biopsy- or cell-based datasets are modules either of the same reference pathway (e.g., metabolism) or of closely interrelated pathways (e.g., thyroid cancer and melanoma). Our reported meta-analysis has revealed novel age-related genes, setting thus the basis for more detailed future functional studies.

A lower-carbohydrate, higher-fat diet reduces abdominal and intermuscular fat and increases insulin sensitivity in adults at risk of type 2 diabetes

BACKGROUND

Obesity, particularly visceral and ectopic adiposity, increases the risk of type 2 diabetes.

OBJECTIVE

The aim of this study was to determine if restriction of dietary carbohydrate is beneficial for body composition and metabolic health.

METHODS

Two studies were conducted. In the first, 69 overweight/obese men and women, 53% of whom were European American (EA) and 47% of whom were African American (AA), were provided with 1 of 2 diets (lower-fat diet: 55%, 18%, and 27% of energy from carbohydrate, protein, and fat, respectively; lower-carbohydrate diet: 43%, 18%, and 39%, respectively) for 8 wk at a eucaloric level and 8 wk at a hypocaloric level. In the second study, 30 women with polycystic ovary syndrome (PCOS) were provided with 2 diets (lower-fat diet: 55%, 18%, and 27% of energy from carbohydrate, protein, and fat, respectively; lower-carbohydrate diet: 41%, 19%, and 40%, respectively) at a eucaloric level for 8 wk in a random-order crossover design.

RESULTS

As previously reported, among overweight/obese adults, after the eucaloric phase, participants who consumed the lower-carbohydrate vs. the lower-fat diet lost more intra-abdominal adipose tissue (IAAT) (11 ± 3% vs. 1 ± 3%; P < 0.05). After weight loss, participants who consumed the lower-carbohydrate diet had 4.4% less total fat mass. Original to this report, across the entire 16-wk study, AAs lost more fat mass with a lower-carbohydrate diet (6.2 vs. 2.9 kg; P < 0.01), whereas EAs showed no difference between diets. As previously reported, among women with PCOS, the lower-carbohydrate arm showed decreased fasting insulin (-2.8 μIU/mL; P < 0.001) and fasting glucose (-4.7 mg/dL; P < 0.01) and increased insulin sensitivity (1.06 arbitrary units; P < 0.05) and "dynamic" β-cell response (96.1 · 10(9); P < 0.001). In the lower-carbohydrate arm, women lost both IAAT (-4.8 cm(2); P < 0.01) and intermuscular fat (-1.2 cm(2); P < 0.01). In the lower-fat arm, women lost lean mass (-0.6 kg; P < 0.05). Original to this report, after the lower-carbohydrate arm, the change in IAAT was positively associated with the change in tumor necrosis factor α (P < 0.05).

CONCLUSION

A modest reduction in dietary carbohydrate has beneficial effects on body composition, fat distribution, and glucose metabolism. This trial was registered at clinicaltrials.gov as NCT00726908 and NCT01028989.

Sex differences in the genome-wide DNA methylation pattern and impact on gene expression, microRNA levels and insulin secretion in human pancreatic islets

Background

Epigenetic factors regulate tissue-specific expression and X-chromosome inactivation. Previous studies have identified epigenetic differences between sexes in some human tissues. However, it is unclear whether epigenetic modifications contribute to sex-specific differences in insulin secretion and metabolism. Here, we investigate the impact of sex on the genome-wide DNA methylation pattern in human pancreatic islets from 53 males and 34 females, and relate the methylome to changes in expression and insulin secretion.

Results

Glucose-stimulated insulin secretion is higher in female versus male islets. Genome-wide DNA methylation data in human islets clusters based on sex. While the chromosome-wide DNA methylation level on the X-chromosome is higher in female versus male islets, the autosomes do not display a global methylation difference between sexes. Methylation of 8,140 individual X-chromosome sites and 470 autosomal sites shows sex-specific differences in human islets. These include sites in/near AR, DUSP9, HNF4A, BCL11A and CDKN2B. 61 X-chromosome genes and 18 autosomal genes display sex-specific differences in both DNA methylation and expression. These include NKAP, SPESP1 and APLN, which exhibited lower expression in females. Functional analyses demonstrate that methylation of NKAP and SPESP1 promoters in vitro suppresses their transcriptional activity. Silencing of Nkap or Apln in clonal beta-cells results in increased insulin secretion. Differential methylation between sexes is associated with altered levels of microRNAs miR-660 and miR-532 and related target genes.

Conclusions

Chromosome-wide and gene-specific sex differences in DNA methylation associate with altered expression and insulin secretion in human islets. Our data demonstrate that epigenetics contribute to sex-specific metabolic phenotypes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0522-z) contains supplementary material, which is available to authorized users.

Food intake does not differ between obese women who are metabolically healthy or abnormal

BACKGROUND

Metabolically healthy obesity may confer lower risk of adverse health outcomes compared with abnormal obesity. Diet and race are postulated to influence the phenotype, but their roles and their interrelations on healthy obesity are unclear.

OBJECTIVE

We evaluated food intakes of metabolically healthy obese women in comparison to intakes of their metabolically healthy normal-weight and metabolically abnormal obese counterparts.

METHODS

This was a cross-sectional study in 6964 women of the REasons for Geographic And Racial Differences in Stroke (REGARDS) study. Participants were aged 45-98 y with a body mass index (BMI; kg/m(2)) ≥18.5 and free of cardiovascular diseases, diabetes, and cancer. Food intake was collected by using a food-frequency questionnaire. BMI phenotypes were defined by using metabolic syndrome (MetS) and homeostasis model assessment of insulin resistance (HOMA-IR) criteria. Mean differences in food intakes among BMI phenotypes were compared by using ANCOVA.

RESULTS

Approximately one-half of obese women (white: 45%; black: 55%) as defined by MetS criteria and approximately one-quarter of obese women (white: 28%; black: 24%) defined on the basis of HOMA-IR values were metabolically healthy. In age-adjusted analyses, healthy obesity and normal weight as defined by both criteria were associated with lower intakes of sugar-sweetened beverages compared with abnormal obesity among both white and black women (P < 0.05). HOMA-IR-defined healthy obesity and normal weight were also associated with higher fruit and low-fat dairy intakes compared with abnormal obesity in white women (P < 0.05). Results were attenuated and became nonsignificant in multivariable-adjusted models that additionally adjusted for BMI, marital status, residential region, education, annual income, alcohol intake, multivitamin use, cigarette smoking status, physical activity, television viewing, high-sensitivity C-reactive protein, menopausal status, hormone therapy, and food intakes.

CONCLUSIONS

Healthy obesity was not associated with a healthier diet. Prospective studies on relations of dietary patterns, which may be a better indicator of usual diet, with the phenotype would be beneficial.

Obesity attenuates gender differences in cardiovascular mortality

Background

To estimate cardiovascular disease (CVD) mortality in relation to obesity and gender.

Methods

Data from 11 prospective cohorts from four European countries including 23 629 men and 21 965 women, aged 24 to 99 years, with a median follow-up of 7.9 years were analyzed. Hazards ratios (HR) for CVD mortality in relation to baseline body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR) and waist-to-height ratio (WHtR) were estimated using Cox proportional hazards models with age as the timescale.

Results

Men had higher CVD mortality than women in all four BMI categories (<25.0, 25.0-29.9, 30.0-34.9 and ≥35.0 kg/m²). Compared with the lowest BMI category in women, multivariable adjusted HRs (95% confidence intervals) for higher BMI categories are 1.0 (0.8-1.4), 1.6 (1.1-2.1) and 2.8 (2.0-3.8) in women and 2.8 (2.2-3.6), 3.1 (2.5-3.9), 3.8 (2.9-4.9) and 5.4 (3.8-7.7) in men, respectively. Similar findings were observed for abdominal obesity defined by WC, WHR or WHtR. The gender difference was slightly smaller in obese than in non-obese individuals; but the interaction was statistically significant only between gender and WC (p = 0.02), and WHtR (p = 0.01). None of the interaction terms was significant among non-diabetic individuals.

Conclusions

Men had higher CVD mortality than women across categories of anthropometric measures of obesity. The gender difference was attenuated in obese individuals, which warrants further investigation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12933-014-0144-5) contains supplementary material, which is available to authorized users.

Assessment of skeletal muscle proteolysis and the regulatory response to nutrition and exercise

Skeletal muscle proteolysis is highly regulated, involving complex intramuscular proteolytic systems that recognize and degrade muscle proteins, and recycle free amino acid precursors for protein synthesis and energy production. Autophagy-lysosomal, calpain, and caspase systems are contributors to muscle proteolysis, although the ubiquitin proteasome system (UPS) is the primary mechanism by which actomyosin fragments are degraded in healthy muscle. The UPS is sensitive to mechanical force and nutritional deprivation, as recent reports have demonstrated increased proteolytic gene expression and activity of the UPS in response to resistance and endurance exercise, and short-term negative energy balance. However, consuming dietary protein alone (or free amino acids), or as a primary component of a mixed meal, may attenuate intramuscular protein loss by down-regulating proteolytic gene expression and the catabolic activity of the UPS. Although these studies provide novel insight regarding the intramuscular regulation of skeletal muscle mass, the role of proteolysis in the regulation of skeletal muscle protein turnover in healthy human muscle is not well described. This article provides a contemporary review of the intramuscular regulation of skeletal muscle proteolysis in healthy muscle, methodological approaches to assess proteolysis, and highlights the effects of nutrition and exercise on skeletal muscle proteolysis.

Physiology of Mechanotransduction: How Do Muscle and Bone "Talk" to One Another?

The complexity of cell interactions with their microenvironment and their ability to communicate at the autocrine, paracrine, and endocrine levels has gradually but significantly evolved in the last three decades. The musculoskeletal system has been historically recognized to be governed by a relationship of proximity and function, chiefly dictated by mechanical forces and the work of gravity itself. In this review article, we first provide a historical overview of the biomechanical theory of bone- muscle interactions. Next, we expand to detail the significant evolution in our understanding of the function of bones and muscles as secretory organs. Then, we review and discuss new evidence in support of a biochemical interaction between these two tissues. We then propose that these two models of interaction are complementary and intertwined providing for a new frontier for the investigation of how bone-muscle cross talk could be fully explored for the targeting of new therapies for musculoskeletal diseases, particularly the twin conditions of aging, osteoporosis and sarcopenia. In the last section, we explore the bone-muscle cross talk in the context of their interactions with other tissues and the global impact of these multi-tissue interactions on chronic diseases.

Whole blood gene expression profiles in insulin resistant Latinos with the metabolic syndrome

Although insulin resistance in skeletal muscle is well-characterized, the role of circulating whole blood in the metabolic syndrome phenotype is not well understood. We set out to test the hypothesis that genes involved in inflammation, insulin signaling and mitochondrial function would be altered in expression in the whole blood of individuals with metabolic syndrome. We further wanted to examine whether similar relationships that we have found previously in skeletal muscle exist in peripheral whole blood cells. All subjects (n=184) were Latino descent from the Arizona Insulin Resistance registry. Subjects were classified based on the metabolic syndrome phenotype according to the National Cholesterol Education Program’s Adult Treatment Panel III. Of the 184 Latino subjects in the study, 74 were classified with the metabolic syndrome and 110 were without. Whole blood gene expression profiling was performed using the Agilent 4x44K Whole Human Genome Microarray. Whole blood microarray analysis identified 1,432 probes that were altered in expression ≥1.2 fold and P<0.05 after Benjamini-Hochberg in the metabolic syndrome subjects. KEGG pathway analysis revealed significant enrichment for pathways including ribosome, oxidative phosphorylation and MAPK signaling (all Benjamini-Hochberg P<0.05). Whole blood mRNA expression changes observed in the microarray data were confirmed by quantitative RT-PCR. Transcription factor binding motif enrichment analysis revealed E2F1, ELK1, NF-kappaB, STAT1 and STAT3 significantly enriched after Bonferroni correction (all P<0.05). The results of the present study demonstrate that whole blood is a useful tissue for studying the metabolic syndrome and its underlying insulin resistance although the relationship between blood and skeletal muscle differs.

Variability in HOMA-IR, lipoprotein profile and selected hormones in young active men

Resistance to insulin actions is contributing to many metabolic disturbances. Such factors as age, sex, nutrition, body fat, and physical activity determine body insulin resistance. Present study attempted to asses insulin resistance and its metabolic effects with respect to energy intake in young, lean, and active men. A total of 87 men aged 18-23 participated in the study. Plasma levels of glucose, insulin, lipoproteins, cortisol, and TSH were determined. Insulin resistance was expressed as Homeostasis Model Assessment for Insulin Resistance (HOMA-IR) and calculated using homeostatic model. The median value of HOMA-IR (1.344) was used to divide subjects into two groups. Men did not differ in anthropometric parameters, daily physical activity, and plasma TSH and cortisol levels. However, in men with higher HOMA-IR significantly lower daily energy intake was observed concomitantly with higher TG, TC, and HDL-C concentrations in plasma versus their counterparts with lower HOMA-IR. Exclusively in subjects with higher HOMA-IR significant and positive correlation was noted between HOMA-IR and TC and LDL-C. We concluded that despite a normal body weight and physical activity, a subset of young men displayed unfavorable changes in insulin sensitivity and lipid profile, probably due to insufficient energy intake.

Body composition and cardiometabolic disease risk factors in captive baboons (Papio hamadryas sp.): sexual dimorphism

Baboons (Papio hamadryas sp.) exhibit significant sexual dimorphism in body size. Sexual dimorphism is also exhibited in a number of circulating factors associated with risk of cardiometabolic disease. We investigated whether sexual dimorphism in body size and composition underlie these differences. We examined data from 28 male and 24 female outdoor group-housed young adult baboons enrolled in a longitudinal observational study of cardiometabolic disease risk factors. Animals were sedated with ketamine HCl (10 mg/kg) before undergoing venous blood draws, basic body measurements, and dual-energy X-ray absorptiometry body composition scans. Percentage glycated hemoglobin A1c (%HbA1c ) was measured in whole blood. Serum samples were analyzed for glucose, insulin, C-peptide, high-density lipoprotein, and triglyceride concentrations. Males were heavier and had greater body length and lean tissue mass than females. Females had a greater body fat percentage relative to males (10.8 ± 6.4 vs. 6.9 ± 4.0, P = 0.01). Although C-peptide, fasting glucose, and %HbA1c did not differ between the sexes, females had greater fasting insulin and triglyceride compared to their male counterparts. Insulin and percentage body fat were significantly correlated in males (r = 0.61, P = 0.001) and to a lesser extent in females (r = 0.43, P = 0.04). Overall, relations between adiposity and fasting insulin and fasting triglyceride were stronger in males. After accounting for differences in percentage body fat, fasting insulin and triglyceride were no longer statistically different between males and females. Despite stronger correlations between relative adiposity and insulin and triglyceride in males, the higher fasting insulin and triglyceride of female baboons may be underlain by their greater relative body fat masses.

Genetic variants associated with fasting glucose and insulin concentrations in an ethnically diverse population: results from the Population Architecture using Genomics and Epidemiology (PAGE) study

BACKGROUND

Multiple genome-wide association studies (GWAS) within European populations have implicated common genetic variants associated with insulin and glucose concentrations. In contrast, few studies have been conducted within minority groups, which carry the highest burden of impaired glucose homeostasis and type 2 diabetes in the U.S.

METHODS

As part of the 'Population Architecture using Genomics and Epidemiology (PAGE) Consortium, we investigated the association of up to 10 GWAS-identified single nucleotide polymorphisms (SNPs) in 8 genetic regions with glucose or insulin concentrations in up to 36,579 non-diabetic subjects including 23,323 European Americans (EA) and 7,526 African Americans (AA), 3,140 Hispanics, 1,779 American Indians (AI), and 811 Asians. We estimated the association between each SNP and fasting glucose or log-transformed fasting insulin, followed by meta-analysis to combine results across PAGE sites.

RESULTS

Overall, our results show that 9/9 GWAS SNPs are associated with glucose in EA (p = 0.04 to 9 × 10-15), versus 3/9 in AA (p= 0.03 to 6 × 10-5), 3/4 SNPs in Hispanics, 2/4 SNPs in AI, and 1/2 SNPs in Asians. For insulin we observed a significant association with rs780094/GCKR in EA, Hispanics and AI only.

CONCLUSIONS

Generalization of results across multiple racial/ethnic groups helps confirm the relevance of some of these loci for glucose and insulin metabolism. Lack of association in non-EA groups may be due to insufficient power, or to unique patterns of linkage disequilibrium.

First steps for integrating sex and gender considerations into basic experimental biomedical research

In recent decades there has been an increasing recognition of the need to account for sex and gender in biology and medicine, in order to develop a more comprehensive understanding of biological phenomena and to address gaps in medical knowledge that have arisen due to a generally masculine bias in research. We have noted that as basic experimental biomedical researchers, we face unique challenges to the incorporation of sex and gender in our work, and that these have remained largely unarticulated, misunderstood, and unaddressed in the literature. Here, we describe some of the specific challenges to the incorporation of sex and gender considerations in research involving cell cultures and laboratory animals. In our view, the mainstreaming of sex and gender considerations in basic biomedical research depends on an approach that will allow scientists to address these issues in ways that do not undermine our ability to pursue our fundamental scientific interests. To that end, we suggest a number of strategies that allow basic experimental researchers to feasibly and meaningfully take sex and gender into account in their work.

Feasibility of using ultrasound to measure preterm body composition and to assess macronutrient influences on tissue accretion rates

BACKGROUND AND AIMS

To assess ultrasound as a method for (i) measuring body composition (BC) of preterm infants and for (ii) assessing the influence of macronutrient intakes on tissue accretion rates.

METHODS

Preterm ultrasound studies of four anatomical sites were performed approximately every three weeks from birth to corrected-term age. Preterm measurements were compared to foetal reference data. Duplicate scans at each site were taken on a subset of infants to test the reproducibility of the method, assessed as the coefficient of variation (CV). The influence of measured macronutrient intakes on preterm BC was assessed by regression analysis.

RESULTS

Median (range) gestation and birth weight of 40 preterm infants were 27 (23-29) weeks and 1022 (480-1475) g, respectively. Accretion rates of adipose and muscle tissues were not uniform across the four sites. Relative to the foetus, preterm adipose tissue thickness was reduced at an equivalent (corrected) gestation, but towards term, a faster accretion rate of subcutaneous abdominal adipose and limb muscle tissue was evident. Timing of fortification (p=0.012), enteral carbohydrate intake (p=0.008) and the protein energy ratio of intakes (p=0.038) moderated the ratio of adipose to muscle tissue accretion over the four sites by -0.004, -0.048 and -0.042, respectively.

CONCLUSIONS

Ultrasound provides a non-invasive, portable method of assessing changes in subcutaneous adipose tissue and muscle accretion and appears sufficiently sensitive to detect influences of macronutrient intakes on accretion rates from birth. The method warrants further investigation as a bedside tool for measuring BC of preterm infants.

Metabolic impact of sex chromosomes

Obesity and associated metabolic diseases are sexually dimorphic. To provide better diagnosis and treatment for both sexes, it is of interest to identify the factors that underlie male/female differences in obesity. Traditionally, sexual dimorphism has been attributed to effects of gonadal hormones, which influence numerous metabolic processes. However, the XX/XY sex chromosome complement is an additional factor that may play a role. Recent data using the four core genotypes mouse model have revealed that sex chromosome complement—independently from gonadal sex—plays a role in adiposity, feeding behavior, fatty liver and glucose homeostasis. Potential mechanisms for the effects of sex chromosome complement include differential gene dosage from X chromosome genes that escape inactivation, and distinct genomic imprints on X chromosomes inherited from maternal or paternal parents. Here we review recent data in mice and humans concerning the potential impact of sex chromosome complement on obesity and metabolic disease.

Women's higher health risks in the obesogenic environment: a gender nutrition approach to metabolic dimorphism with predictive, preventive, and personalised medicine

Women's evolution for nurturing and fat accumulation, which historically yielded health and longevity advantages against scarcity, may now be counteracted by increasing risks in the obesogenic environment, recently shown by narrowing gender health gap. Women's differential metabolism/disease risks, i.e. in fat accumulation/distribution, exemplified during puberty/adolescence, suggest gender dimorphism with obesity outcomes. Women's higher body fat percentage than men, even with equal body mass index, may be a better risk predictor. Differential metabolic responses to weight-reduction diets, with women's lower abdominal fat loss, better response to high-protein vs. high-carbohydrate diets, higher risks with sedentariness vs. exercise benefits, and tendency toward delayed manifestation of central obesity, metabolic syndrome, diabetes, cardiovascular disease, and certain cancers until menopause-but accelerated thereafter-suggest a need for differing metabolic and chronological perspectives for prevention/intervention. These perspectives, including women's differential responses to lifestyle changes, strongly support further research with a gender nutrition emphasis within predictive, preventive, and personalized medicine.

Inhibition of gastric lipase as a mechanism for body weight and plasma lipids reduction in Zucker rats fed a rosemary extract rich in carnosic acid

Background

Rosemary (Rosmarinus officinalis L.) extracts (REs) exhibit hepatoprotective, anti-obesity and anti-inflammatory properties and are widely used in the food industry. REs are rich in carnosic acid (CA) and carnosol which may be responsible for some of the biological activities of REs. The aim of this study was to investigate whether inhibition of lipase activity in the gut may be a mechanism by which a RE enriched in CA (40%) modulates body weight and lipids levels in a rat model of metabolic disorders and obesity.

Methods and Principal Findings

RE was administered for 64 days to lean (fa/+) and obese (fa/fa) female Zucker rats and body weight, food intake, feces weight and blood biochemical parameters were monitored throughout the study. Lipase activity (hydrolysis of p-nitrophenylbutyrate) was measured in the gastrointestinal tract at the end of the study and the contents of CA, carnosol and methyl carnosate were also determined. Sub-chronic administration of RE moderately reduced body weight gain in both lean and obese animals but did not affect food intake. Serum triglycerides, cholesterol and insulin levels were also markedly decreased in the lean animals supplemented with RE. Importantly, lipase activity was significantly inhibited in the stomach of the RE-supplemented animals where the highest content of intact CA and carnosol was detected.

Conclusions

Our results confirm that long-term administration of RE enriched in CA moderates weight gain and improves the plasma lipids profile, primarily in the lean animals. Our data also suggest that these effects may be caused, at least in part, by a significant inhibition of gastric lipase and subsequent reduction in fat absorption.

Sex differences in human adipose tissues - the biology of pear shape

Women have more body fat than men, but in contrast to the deleterious metabolic consequences of the central obesity typical of men, the pear-shaped body fat distribution of many women is associated with lower cardiometabolic risk. To understand the mechanisms regulating adiposity and adipose tissue distribution in men and women, significant research attention has focused on comparing adipocyte morphological and metabolic properties, as well as the capacity of preadipocytes derived from different depots for proliferation and differentiation. Available evidence points to possible intrinsic, cell autonomous differences in preadipocytes and adipocytes, as well as modulatory roles for sex steroids, the microenvironment within each adipose tissue, and developmental factors. Gluteal-femoral adipose tissues of women may simply provide a safe lipid reservoir for excess energy, or they may directly regulate systemic metabolism via release of metabolic products or adipokines. We provide a brief overview of the relationship of fat distribution to metabolic health in men and women, and then focus on mechanisms underlying sex differences in adipose tissue biology.

Comparison of insulin action on glucose versus potassium uptake in humans

BACKGROUND AND OBJECTIVES

Insulin has several physiologic actions that include stimulation of cellular glucose and potassium uptake. The ability of insulin to induce glucose uptake by cells is impaired in type 2 diabetes mellitus, but whether potassium uptake is similarly impaired is not known. This study examines whether the cellular uptake of these molecules is regulated in concert or independently.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Thirty-two nondiabetic and 13 type 2 diabetic subjects with normal GFR were given a similar, constant metabolic diet for 8 days. On day 9, they were subjected to a hyperinsulinemic euglycemic clamp for 2 hours. Serum and urinary chemistry were obtained before and during the clamp. Glucose disposal rate was calculated from glucose infusion rate during hyperinsulinemic euglycemia. Intracellular potassium and phosphate uptake were calculated by the reduction of extracellular potassium or phosphate content corrected for urinary excretion.

RESULTS

Although glucose disposal rate tended to be lower in type 2 diabetics, cellular potassium uptake was similar between diabetics and nondiabetics. Additionally, although glucose disposal rate was lower with increasing body mass index (R² = 0.362), cellular potassium (R² = 0.052), and phosphate (R² = 0.002), uptake rates did not correlate with body mass index. There was also no correlation between glucose disposal rate and potassium (R² = 0.016) or phosphate uptake (R² = 0.053). Conclusions Insulin-stimulated intracellular uptake of glucose and potassium are independent of each other. In type 2 diabetes, potassium uptake is preserved despite impaired glucose disposal.

Fuel selection and appetite-regulating hormones after intake of a soy protein-based meal replacement

OBJECTIVE

The present study investigated the postprandial glycemic and insulinemic responses, the levels of satiety-related proteins, and substrate use after a single dose of a meal replacement (MR) with a high soy protein content and a low glycemic index (GI). The results were compared with a standardized breakfast showing a high GI and a low protein content.

METHODS

Eleven overweight or obese male subjects with the metabolic syndrome and insulin resistance were included in the study. In the morning, each subject consumed, in a randomized design, 65 g of a MR or an isocaloric standardized breakfast. Four hours after breakfast, all subjects consumed the same standardized lunch. Blood levels of glucose, insulin, ghrelin, protein YY(PYY), oxygen uptake, and carbon dioxide production were determined and the respiratory quotient and substrate use were calculated.

RESULTS

The glycemic and insulinemic responses were considerably higher after the standardized breakfast. In addition, in these obese insulin-resistant subjects, the postprandial decease in fat oxidation was significantly less pronounced after intake of the MR. This effect was also detectable after lunch in terms of a second meal effect. Ghrelin levels were significantly lower 2 h after the intake of the MR and PYY levels tended higher.

CONCLUSION

Compared with the high GI/low-protein SB, a high soy protein MR with a low GI was associated with lower glycemia and insulinemia and relatively higher fat oxidation in the postprandial period. Together with a favorable course of appetite-regulating hormones, this could further help to explain the beneficial role of MR regimines high in soy protein for weight reduction and improvement of metabolic risk factors.

Association between insulin resistance and lean mass loss and fat mass gain in older men without diabetes mellitus

OBJECTIVES

To examine the associations between insulin resistance and changes in body composition in older men without diabetes mellitus.

DESIGN

Longitudinal cohort study of older men participating in the Osteoporotic Fractures in Men (MrOS) study.

SETTING

Six U.S. clinical centers.

PARTICIPANTS

Three thousand one hundred thirty-two ambulatory men aged 65 and older at baseline.

MEASUREMENTS

Baseline insulin resistance was calculated for men without diabetes mellitus using the homeostasis model assessment of insulin resistance (HOMA-IR). Total lean, appendicular lean, total fat, and truncal fat mass were measured using dual energy X-ray absorptiometry scans at baseline and 4.6 ± 0.3 years later in 3,132 men with HOMA-IR measurements.

RESULTS

There was greater loss of weight, total lean mass, and appendicular lean mass and less gain in total fat mass and truncal fat mass with increasing quartiles of HOMA-IR (P<.001 for trend). Insulin-resistant men in the highest quartile had higher odds of 5% or more loss of weight (odds ratio (OR)=1.88, 95% confidence interval (CI)=1.46-2.43), total lean mass (OR=2.09, 95% CI=1.60-2.73) and appendicular lean mass (OR=1.57, 95% CI=1.27-1.95) and lower odds of 5% or more gain in total fat mass (OR=0.56, 95% CI=0.45-0.68) and truncal fat mass (OR=0.52, 95% CI=0.42-0.64) than those in the lowest quartile. These findings remained significant after accounting for age, site, baseline weight, physical activity, and change in physical activity. These associations were also independent of other metabolic syndrome features and medications.

CONCLUSION

Greater lean mass loss and lower fat mass gain occurred in insulin-resistant men without diabetes mellitus than in insulin-sensitive men. Insulin resistance may accelerate age-related sarcopenia.

Sex differences in lipid and lipoprotein metabolism: it's not just about sex hormones

It is commonly thought that sex hormones are important regulators of plasma lipid kinetics and are responsible for sexual dimorphism in the plasma lipid profile. Here we discuss the findings from studies evaluating lipid and lipoprotein kinetics in men and women in the context of what we know about the effects of exogenous sex hormone administration, and we conclude that it is more complicated than that. It has become clear that normal physiological alterations in the hormonal milieu (i.e. due to menopause or throughout the menstrual cycle) do not significantly affect plasma lipid homeostasis. Furthermore, parenterally administered estrogens have either no effect or only very small beneficial effects, whereas orally administered estrogens raise plasma triglyceride concentrations--a phenomenon that is not consistent with the observed sex differences and likely results from the hepatic "first-pass effect." The effects of progestogens and androgens mimic only in part the differences in plasma lipids between men and women. Thus, the underlying physiological modulators of plasma lipid metabolism responsible for the differences between men and women remain to be elucidated.

Reproducibility of glucose, fatty acid and VLDL kinetics and multi-organ insulin sensitivity in obese subjects with non-alcoholic fatty liver disease

OBJECTIVE

Non-alcoholic fatty liver disease (NAFLD) is associated with abnormalities in basal glucose and free fatty acid (FFA) metabolism, multi-organ insulin resistance and alterations in lipoprotein kinetics. These metabolic outcomes can be evaluated in vivo by using stable isotopically labeled tracer methods. An understanding of the reproducibility of these measures is necessary to ensure adequate statistical power in studies designed to evaluate metabolic function in subjects with NAFLD.

METHODS

We determined the degree of intra-individual variability of skeletal muscle, adipose tissue, and hepatic insulin sensitivity and basal plasma glucose, FFA, and very-low-density lipoprotein triglyceride and apolipoprotein B-100 (apoB-100) kinetics in eight obese subjects with NAFLD (age: 44 ± 3 years; body mass index: 38.2 ± 1.7 kg m(-2); intrahepatic triglyceride content: 24.5 ± 3.9%), by using the hyperinsulinemic-euglycemic clamp technique and stable isotope-labeled tracer methods and mathematical modeling on two separate occasions ∼2 months apart.

RESULTS

The intra-individual variability (coefficient of variation) ranged from 6% for basal glucose production to 21% for insulin-stimulated glucose disposal (percentage increase from basal). We estimated that a 25% difference in any outcome measure can be detected with a sample size of ≤ 8 subjects for paired studies and ≤ 15 subjects per group for unpaired studies, assuming an α value of 0.05 and a β value of 0.20 (that is, 80% power).

CONCLUSION

These results demonstrate that only a small number of subjects are needed to detect clinically relevant effects in insulin sensitivity and hepatic lipoprotein metabolism in obese subjects with NAFLD, and will be useful to determine appropriate sample size for future metabolic studies.

Relationships of cardiorespiratory fitness with metabolic risk factors, inflammation, and liver transaminases in overweight youths

The aim of this study was to assess the relationships of fatness and fitness with metabolic risk factors, including liver transaminases and inflammation in obese youth, taking in account gender, age, and pubertal stage. 241 children were studied (135 girls), age 11.9 +/- 2.2 years (x +/- SD), Body Mass Index z score 5.4 +/- 2.7. For girls, VO(2max) was significantly associated with insulin (P = .001), Insulin resistance (HOMA-IR) (P = .005), and ALT (P = .012); a relationship was displayed between fibrinogen and age and % fat mass (FM) (P = .008); for boys, relationships were found between VO(2max) and diastolic blood pressure and triglycerides; independent associations were also found between age and insulin, HOMA-IR and HDL cholesterol; fibrinogen and sedimentation rate were related (P </= .004) with %FM. Their relationships are observed from young age and increase with the continuous increase of factors. This supports the need to treat overweight as soon as it is detected; improving CRF is one of the ways which could be used to prevent the complications of obesity.